Cat attacked my neice and me

About a month ago, my roommate hit a puppy with his truck by accident
and we brought it home to try to save it but didn't have any luck. We have two cats, one male and one female, and now have 4 kittens. The male is two weeks older than the female and is about 9 months old. When we brought the puppy home the female freaked out and ran away from the puppy and everyone. The puppy's scent and blood got on my roommates sweater and we have washed it about 5-6 times since the incident. Yesterday he went to wash his clothes and was dragging the sleeve of the sweater when the female (pepper) must of smelled the scent and went crazy. A little while later, when she was still in her "defensive", I went to calm her down and she ran away and attacked my neice who was on the other side of the room. She scratched my neices arms and almost got her eye. About an hour later, I went to seperate my other cat from her and she attacked my leg twice for no reason. Since then we have locked her in the bathroom untill we go and get both of them fixed. Please give me any advice you may have on why pepper did this and what we can do to prevent this from happening again.

I think you answered your own question - it scared the living daylights out of her. Cat's sense of smell is much much better than a humans and washing the sweater is not going to do it. She needs time to calm down and lots of reasurance and love from you telling her everything is ok.

Hide the sweater for a while - she is probably terrified especially if she just had kittens - she feels she has to protect them.

Most cats when upset, aggrivated, angry or frustrated will re direct the aggresion to anyone or anything in the near vicinity. They really can't help it because they have no other way to express these emotions. The few things you can try is getting her spayed asap so that the hormone level evens out, try to reduce the amount of stress by maybe just getting rid of this particular sweater oe have a medium sized stuff animal handy for when you see her go into these attack modes. You can pass this off to her and she will probably let her frustrations out on it rather than you.

Also take the sweater and wash it and add with the detergent about a cup of regular vinegar. After it is washed, hang it out in the air for several days to get all the smells out of it and that should stop the cats reaction. The smell of blood will freak out any animal, be it dog, cat or even horse. Mom needs to protect her young and that is what she is doing. And please get her spayed as soon as you can, that will help as well